1. Field of the Invention
The present invention relates generally to strengthening members for use in retaining building roofs, and in particular to a tie-down member specially configured to restrain roof trusses under heavy wind conditions as encountered in hurricane prone regions.
2. Description of the Prior Art
Methods and apparatus for providing metallic strengthening and interconnecting elements for use with wooden building components have a long history of development. Craftsmen and tradesmen in the construction field have directed a good deal of attention to families of interconnecting devices including joist hangers, stud holders, and brackets of all types. Upon close review, however, the greatest majority of prior art teachings in this area are directed to brackets and hangers adapted to operate against static gravity loads. The straightforward requirements of supporting more or less constant gravity-induced loads have produced a number of well-known and widely used devices. The problems associated with dynamically induced uplift forces in buildings--especially those with pitched roofs--have not been adequately addressed by prior art devices. This fact is attested to by the severe property losses experienced regularly in regions of the country that are subjected to seasonal wind storms or recurring hurricane conditions.
Descriptions of typical prior art approaches to the roof uplift problem may be found in a number of U.S. patents. Illustrative early teachings of metallic members used to tie down roof rafters are found in U.S. Pat. Nos. 1,277,766 to Stadelman and 1,657,441 to Huovinen. In the 1918 '766 patent, a simple wrought iron strap (single length, quarter-turn twist) is bolted to a vertical wall member at a lower end and to a rafter at an upper end as a `preferred means` of connection between the roof and siding. The 1928 '441 patent shows the use of a pair of similar metallic strap-like members bolted to each rafter just above where they meet a masonry block wall, the straps continuing downward through the courses of block to ultimately be anchored in a concrete footing.
An even earlier teaching of a two-part metallic member used to fasten upright posts to rafters is provided in U.S. Pat. No. 1,179,785 issued in 1916 to Walker. In this patent, each of two mirror image metal bars are riveted to opposite sides of the post tops and extend over the top of a rafter to meet clam-shell like at the rafter top surface.
A more recent teaching of retaining rafters in a pole barn is found in U.S. Pat. No. 2,843,085 issued in 1958 to McKee. No substantive details on the structure of the strap iron member are found, and from the drawing it appears to be a simple wrap-around and nail-down device.
Present-day approaches to this critical area continue to be largely ad hoc and vary widely between seriously underestimating the dynamic requirements involved, and using greatly over-designed, brute force tie-downs. Consider the more or less contemporary approach found in U.S. Pat. No. 4,478,018 to Holland. Specifically reciting hurricane requirements for restraining roof structures, steel straps riveted to metallic top channels positioned over the entire length of vertical walls are employed. Other contemporary approaches alternatively employ L-shaped brackets of 3/8-inch steel, the brackets held to the roof trusses by an unseemly large number of nails.
Clearly, current approaches to securing roofs to their associated buildings continue to reflect a lack of appreciation for this critical task. In those areas of the country where hurricane-level winds occur, the failure of roof truss anchoring means is dramatically seen on a year-after-year basis.
Therefore, the improved hurricane tie-down member as taught in the present invention admirably addresses the roof truss uplift problems associated with pitched roofs and provides significant benefits in this usage while retaining all of the desirable low-cost and simple-to-use attributes.